Sealing device for rotary feedthrough

ABSTRACT

A sealing device for a rotary feedthrough for receiving a rotating machine element whose outer side can be applied to another machine element includes at least two sealing elements disposed in tandem in the axial direction of the machine element. Inner sides of the sealing elements are configured for forming an active sealing connection with the rotating machine element. At least one of the sealing elements can be pressurized with an additional force acting in the radial direction so that the force of compression acting on the rotating machine element for the at least one of the sealing elements can be adjusted relative to the force of compression acting on the rotating machine element due to at least one other sealing element.

The invention relates to a sealing device for a rotary feedthrough as isused, for example, in vacuum-processing facilities for coatingsubstrates.

Rotary feedthroughs are needed in order to feed rotating parts (such as,for example, shafts) through housing walls and the like when the drivingmachine element, e.g. a drive device, is disposed on one side of thehousing wall and the machine element to be driven, e.g. a rotatingtarget, is disposed on the other side of the housing wall.

If a pressure differential must be maintained between the two sides ofthe housing wall (for example, atmospheric pressure on one side, highvacuum on the other side) and/or the atmospheres on the two sides of thehousing walls have different compositions (for example, air on one side,inert gas on the other side), then it is necessary to configure therotary feedthrough so that one prevents an undesired equalization ofpressure or an exchange of gas between the two sides of the housing walldue to leakage in the rotary feedthrough.

Rotary feedthroughs for vacuum facilities can, for example, comprise twoseals acting in tandem, where one seal is disposed so that it sealstowards the atmosphere and the other seal is disposed so that it sealstowards the vacuum or the process atmosphere. Between these two seals acomplete separation of the media can be achieved, for example, with asealing medium, that is, a sealing gas or a sealing liquid.Alternatively, separation of an atmosphere and a processing space can beachieved with an intermediate vacuum generated between both seals.

It is known that at higher rate of flow of alternating current throughthe shaft all the electrically conductive components which encircle theshaft in the manner of a ring can heat up to the point of destructiondue to self-induction. This has as a consequence the fact that, in theselection of seals, springs, or supporting rings which encircle theshaft, attention must be paid to the fact that they have to be ofnon-conductive material or interrupted in their circumference.

It is also known that the sealing materials to be used must have goodsliding properties in dry operation. This requirement can, for example,be met with the material PTFE with portions of graphite, molybdenumdisulphide, or bronzes. The shaft surface can, for example, be coatedwith chromium oxide, which, in given cases, can be sealed with phenolicresin, thus attaining a very high strength of sealing.

However, several vacuum processes using large amounts of oxygen requirea seal free of sealing media and cannot consist of oxidizing materials.For these instances of use, the sealing material PTFE with portions ofpolyoxybenzoyl ester combined with a countersurface of chromium oxidesealed with phenolic resin has proven itself effective. In that case theseal runs on the chromium oxide layer without lubrication.

In order to achieve a sufficient sealing effect, sealing elements of thesealing device can be provided, for example, with a sealing lip. Suchsealing lips can, for example, be generated by using as a sealingelement a circular ring disc whose inner diameter is less than the outerdiameter of the rotating machine element which projects through therotary feedthrough. Along with this there is a sealing gap between thesealing lip and the rotating machine element, said sealing gap beingunder intrinsic tension.

The atmospheric pressure which is present and the intermediate vacuumwhich is present generate in addition a pressure load on the sealinglip. Under the different pressure loads of the two sealing lips,different wear of the same arises towards the sliding surface. However,wear is of decisive importance for the service lifetime of the sealingdevice.

In the selection of the sealing materials of the sealing lips one mustpay attention to the properties of good restoration properties, lowwear, and good sliding characteristics. Problematic in the selection ofthe sealing materials is the fact that all the properties have mutualinteractions.

The envisioned sealing combinations have the disadvantage that thesealing lip disposed nearer to the vacuum, due to the lower forces ofcompression, produces a lower sealing action and the sealing lipdisposed nearer to the atmosphere experiences higher wear.

One object is thus to fashion a sealing combination which simultaneouslyhas good sliding characteristics and low wear and achieves a longservice lifetime of the rotary feedthrough. The wear of both sealsshould be matched and the sealing action of the sealing combinationshould be increased.

For this purpose it is first of all proposed that for the seals, or thesealing elements comprised therein, materials be selected which havegood sliding characteristics and low wear. Moreover, it is proposed toactively affect the relationship of the forces of compression which areexerted on the rotating machine element by the sealing elements in thatit is provided that an additional force is applied at least to onesealing element. The additional force can be constant, for example, by aspring element being used which encircles the sealing element and ismanufactured of a non-conductive material with elastic properties, forexample, a polymer. This can, for example, be an O-ring or a specialring with a rectangular cross section, where the diameter is chosen sothat the ring in the installed state is preloaded and in this way aconstant additional force acting in the radial direction on the sealingelement is generated (FIGS. 1, 2, 3). By an appropriate design themagnitude of the additional force thus generated can be set.

The spring element can also consist of a metallic annular spring whichis interrupted in a contact-free manner at least one point.

A variable, and thus also dynamically adjustable, additional force canbe generated if a cavity encircling the sealing element is provided,said cavity being pressurized with a selectable internal pressure. Thiscan be formed by the sealing element itself, for example, by the sealingelement being a tube which is adjacent to the rotating machine element.The sealing element can also be a tube which is provided in addition andis adjacent to the sealing element (FIG. 4). Finally, it can be providedthat the sealing element participates in the formation of the springelement in working together with other components, e.g. an additionalring which is also a part of the sealing device, so that the sealingelement acts as a membrane which generates an additional radial force onthe rotating machine element, said radial force being a function of theinternal pressure of the cavity formed (FIG. 5).

In the embodiment examples presented the necessary preloading of thesealing lips is achieved via the atmospheric pressure and in the area ofthe intermediate vacuum by means of a spring element. The spring elementis designed so that in total the generated force of compression on onesealing element is the same as the force of compression on the othersealing element, that force of compression being caused by theatmospheric pressure. Since the same forces act on both sealingelements, a maximum sealing with equal wear is achieved.

In the following the invention will be explained in more detail with theaid of embodiment examples and corresponding drawings. Therein

FIG. 1 shows a first embodiment example in which the additional force ofa sealing element is generated by a spring element and the atmosphericpressure acting thereon,

FIG. 2 shows a second embodiment example in which the additional forceof a sealing element is generated by a mechanically preloaded springelement,

FIG. 3 shows a third embodiment example in which the sealing element isembodied as one piece,

FIG. 4 shows a fourth embodiment example in which the spring element isa tube provided in addition and adjacent to the sealing element,

FIG. 5 shows a fifth embodiment example in which the sealing elementforms a cavity whose internal pressure communicating with the atmospheregenerates the additional force,

FIG. 6 shows a sixth embodiment example in which the sealing elementforms a cavity whose internal pressure communicating with the atmospheregenerates the additional force.

The embodiment examples of FIGS. 1 to 4 each show a sealing devicecomprising two sealing elements 7 and 8 disposed in tandem in the axialdirection with sealing lips 9 turned up and an intermediate suctionelement disposed between the two sealing element 7 and 8 for generatinga fore vacuum and intermediate vacuum. Through the additionally providedspring element 13 the compressive force of the inner sealing element 7disposed nearer to the vacuum acts on the shaft 3.

In FIG. 1 the sealing device comprises several components disposed intandem in a bearing seat 1 and held in position with a flange 2 withconcentric openings through which a shaft 3 can be fed. These componentscomprise an inner limiting ring 4, a central limiting ring 5, and anouter limiting ring 6, where the inner limiting ring 4 is disposed onthe side of the vacuum and the outer limiting ring 6 is disposed on theside of the atmosphere as well as an inner sealing element 7 disposedbetween the inner limiting ring 4 and the central limiting ring 5 and anouter sealing element 8 disposed between the central limiting ring 5 andthe outer limiting ring 6.

The inner sealing element 7 and the outer sealing element 8 are eachembodied as flat circular ring disc whose inner diameter is less thanthe outer diameter of the shaft 3 so that the inner edge of the circularring disc is turned up and thus forms a sealing lip 9 abutting the shaft3.

The limiting rings 4, 5, and 6 comprise, at suitable points, groovesinto which O-rings 10 are laid which serve for sealing the limitingrings 4, 5, and 6 against one another or against the sealing elements 7and 8 as well as against the bearing seat 1.

The central limiting ring 5 comprises two holes which on one side emptybetween the inner sealing element 7 and the outer sealing element 8 andon the other side are connected to channels which are provided in thebearing seat 1. These are a gas intake duct 11 and a gas suction duct12. The suction duct 12 serves to generate a fore vacuum or intermediatevacuum between the inner sealing element 7 and the outer sealing element8. The gas intake duct 11 on the contrary communicates with theatmosphere so that in the area of its port between the inner sealingelement 7 and the outer sealing element 8 atmospheric pressure prevails.

Between the port of the gas intake duct 11 and the turned-up sealing lip9 of the inner sealing element 7 an annular spring element 13 and amembrane ring 14 are disposed. The membrane ring has the object ofsealing the gas intake duct 11 with respect to the sealing lip 9, thesealing lip 9 of the inner sealing element 7 lying in the area of thefore vacuum generated by the gas suction duct, and simultaneouslytransmitting the atmospheric pressure to the spring element 13.

In this way the atmospheric pressure is transmitted through the gasintake duct over the membrane ring 14 and the spring element 13 to thesealing lip 9 of the inner sealing element 7 although at the sealing lip9 of the inner sealing element 7 the pressure of the fore vacuum ispresent. Thus the pressure on the sealing lip 9 of the inner sealingelement 7 is just as great as on the sealing lip 9 of the outer sealingelement 8 which is directly exposed to the atmospheric pressure.

The embodiment example represented in FIG. 2 is distinguished from theembodiment example above by the fact that no gas intake duct 11 ispresent. Instead of this, the spring element 13 is disposed between thecentral limiting ring 5 and the sealing lip 9 of the inner sealingelement 7 and in fact so that the spring element 13 is preloaded. Thiscan be achieved by a suitable choice of the inner diameter of thecentral limiting ring 5, of the outer diameter of the sealing lip 9 ofthe inner sealing element 7, and the thickness of the spring element 13.In so doing, the preloading can be set so that the preloading of thespring element 13 generates an additional force on the sealing lip 9 ofthe inner sealing element 7, said additional force corresponding to theradial force generated by the atmospheric pressure which is acting onthe sealing lip 9 of the outer sealing element 8.

In the embodiment example according to FIG. 3 the additional force onthe sealing lip 9 of the inner sealing element 7 is generated in amanner analogous to the embodiment example according to FIG. 2, namelyby mechanical preloading between the sealing lip 9 and a limiting ring.In this case however it is the inner limiting ring 4. A central limitingring is not provided. In this development the inner limiting ring 4 issimultaneously the inner sealing element 7, that is, the sealing element7 is not embodied as a separate, flat circular ring disc but rather isintegrated into the inner limiting ring 4. In the same manner the outersealing element 8 with the sealing lip 9 is an integral component of theouter limiting ring 6.

In FIG. 4 a further embodiment example is represented in which a tube 15is inserted into the gas intake duct 11, said tube being adjacent to thesealing lip 9 of the inner sealing element 7 in the interior of thecentral limiting ring 5. Due to the difference in pressure between theatmospheric pressure within the tube 15 and the fore vacuum outside ofthe tube 15 the tube 15 inflates and thus generates an additional radialforce on the sealing lip 9 of the inner sealing element 7.

In the embodiment example according to FIG. 5 an auxiliary ring 16 isdisposed between the inner limiting ring 4 and the central limiting ring5, said auxiliary ring comprising the hole connected to the gas intakeduct 11. This hole empties into the interior of an inner sealing element7 which is U-shaped in longitudinal section so that the atmosphericpressure acts on the lower area of the U-shaped cross section and thusthere is generated an additional radial force on this lower areagenerating the sealing action with respect to the shaft 3.

In the embodiment example according to FIG. 5 the inner sealing element7 disposed nearer to the vacuum, together with the adjacent auxiliaryring 16, forms a spring element with a cavity, where the adjacentauxiliary ring 16 comprises a hole through which the cavity communicateswith the gas intake duct 11 and in this way with the atmosphere. Betweenthe two sealing elements 7 and 8 a gas suction duct 12 is in turndisposed for generating a fore vacuum or an intermediate vacuum.

A similar development of a sealing device is represented in FIG. 6.Therein the inner limiting ring 4 itself forms the inner sealing element7. A central limiting ring 5 is not needed. The auxiliary ring 16 isembedded in the inner limiting ring 4, that is, the auxiliary ring 16 isencircled by the inner limiting ring 4. The inner sealing element 7disposed nearer to the vacuum, together with the encircled auxiliaryring 16, forms a spring element with a cavity, where the encircledauxiliary ring 16 comprises a hole through which the cavity communicateswith the gas intake duct 11 and in this way with the atmosphere. Theatmospheric pressure acts on the lower area of the inner sealing element7 and thus there is generated an additional radial force on this lowerarea, said radial force generating the sealing action with respect tothe shaft 3. Between the two sealing elements 7 and 8 there is disposedin turn a gas suction duct 12 for generating a fore vacuum and anintermediate vacuum, said duct emptying in the embodiment example in thearea of the outer sealing element 8 with the sealing lip 9.

Sealing Device for a Rotary Feedthrough LIST OF REFERENCE NUMBERS

-   -   1 Bearing seat    -   2 Flange    -   3 Shaft    -   4 Inner limiting ring    -   5 Central limiting ring    -   6 Outer limiting ring    -   7 Inner sealing element    -   8 Outer sealing element    -   9 Sealing lip    -   10 O-Ring    -   11 Gas intake duct    -   12 Gas suction duct    -   13 Spring element    -   14 Membrane ring    -   15 Tube    -   16 Auxiliary ring

1. Sealing device for a rotary feedthrough for receiving a rotatingmachine element whose outer side can be applied to another machineelement, comprising at least two sealing elements disposed in tandem inan axial direction of the rotating machine element, the at least twosealing elements having inner sides configured for forming an activesealing connection with the rotating machine element, and means forpressurizing at least one of the sealing elements with an additionalforce acting in a radial direction so that force of compression actingon the rotating machine element for the at least one of the sealingelements relative to force of compression acting on the rotating machineelement for at least one other of the sealing elements can be adjusted.2. Sealing device according to claim 1, wherein the means forpressurizing with the additional force comprises a spring element. 3.Sealing device according to claim 2, wherein the spring element isadjacent to the at least one of the sealing elements and is manufacturedof a non-conductive material.
 4. Sealing device according to claim 2,wherein the spring element comprises a ring of a polymer material. 5.Sealing device according to claim 2, wherein the at least one of thesealing elements itself forms the spring element and comprises a cavitypressurized with an internal pressure.
 6. Sealing device according toclaim 2, wherein the at least one of the sealing elements participatesin the formation of the spring element with a cavity which can bepressurized with an internal pressure.
 7. Sealing device according toclaim 2, wherein between two of the sealing elements at least one gassuction duct for generating a low pressure is disposed.
 8. Sealingdevice according to claim 7 wherein said at least one as suction ductgenerates an intermediate vacuum.